Miniature low frequency transformer



1967 KIYOTAKA NAITO E MINIATURE LOW FREQUENCY TRANSFORMER 7 Sheets-Sheet 1 Filed Oct. 22, 1965 FIG.

FIG 2 PRIOR ART FIG. 3

Dec. 12, 1967 KWOTAKA NAITO ET AL 3,358,256

MINIATURE LOW FREQUENCY TRANSFORMER Filed Oct. 22, 1965 7 Sheets-Sheet :3

Dec. 12, 1967 K|YOTAKA NAITO ET AL MINIATURE LOW FREQUENCY TRANSFORMER Filed Oct. 22, 1965 7 Sheets-Sheet 5 Dec. 12, 1967 K|YOTAKA NAITO ET AL 3,358,256

MINIATURE LOW FREQUENCY TRANSFORMER Filed Oct. 22, 1965 FIG.12

7 Sheets-Sheet 4 Dec. 12, 1967 KWOTAKA NAlTQ ET AL 3,358,256

MINIATURE LOW FREQUENCY TRANSFORMER 7 Sheets-Sheet 6 Filed Oct. 22, 1965 FIG. I7

----- PRIOR ART .THIS INVENTION FREOUENCY(C/S) m 9 a 7 a 5 4 a 2 ..I 0 fix. mohoqm ZOCKOFQQ Dec. 12, 1967 AKA NAITO ETAL 3,358,256

MINIATURE LOW FREQUENCY TRANSFORMER Filed Oct. 22, 1965 7 eet I;

PRIOR ART THIS INVENTION PRIOR THIS IN TION United States Patent Office 3,35%,256 MINIATURE LOW FREQUENCY TRANSFORMER Kiyotaka Naito, Fuhnshima-lren, Hirohiiro Matsunaga, Musashino-shi, Masao Izawa, Nerima-kn, Tokyo, and Hitosi Kanelto, Hino-shi, Toyko, Japan, assignors to Sansni Electric Co. Ltd, Tokyo, Japan, a corporation of Japan Fiied Oct. 22, 1965, Ser. No. 501,911 Claims priority, application Japan, Apr. 3, 1965, til/20,725 4 Claims. (Cl. 336-83) ABSTRACT OF THE DISCLOSURE In this transformer, there is a central cylinder with annular flanges extending from each end of the cylinder. This cylinder with its flanges is placed in a box-like outer core integrally fabricated of a single piece of solid thin sheet material having high magnetic permeability. The box-like outer core supports a terminal plate, and a winding is wound around the cylinder, the end leads being connected to the terminals of the terminal plate.

This invention relates to a miniature low frequency transformer having improved transmission characteristic through the improvement of the effective permeability of the magnetic core.

The features and advantages of this invention will become apparent upon consideration of the following detailed description of this invention, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view showing a cylindrical bobbin of the conventional miniature transformer;

FIG. 2 is a longitudinal section of the bobbin of FIG. 1 wound by acoil;

FIG. 3 is a perspective view showing a sleeve placed over the bobbin shown in FIG. 2;

FIG. 4 is an exterior view in perspective of the conventional miniature transformer;

FIG. 5 is a perspective view showing one embodiment of the inner core utilized in the transformer of this invention;

FIGS. 69 are bodiments of the of this invention;

FIG. 10 is a perspective view showing one embodiment of an outer core utilized in the transformer of this invention;

FIG. 11 is a longitudinal section of the inner core taken along the line of A-A of FIG. 8;

FIG. 12 is a perspective view showing the inner core of FIG. 9 secured within the outer core of FIG. 10;

FIG. 13 is an analytical view in perspective of the construction process of the transformer in accordance with this invention;

FIG. 14 is an exterior view in perspective of one embodiment of the transformer in accordance with this invention;

FIG. 15 is a view showing the difference between the frequency characteristic of the conventional transformer shown in FIG. 4 and that of the transformer of this invention;

FIG. 16 is a view showing the difference between the distortion factor characteristic of the conventional transformer utilizing an E and an I type cores and that of the transformer in accordance with this invention;

FIG. 17 is a similar view showing the difference between the distortion factor characteristic of the transformer shown in FIG. 4 and that of the transformer in accordance with this invention; and

perspective views showing other eminner core utilized in the transformer 3,358,256 Fatented Dec. 12, 1967 FIG. 18 is a view showing the difference between the shielding efliciency of the conventional transformer utilizing an E and an I type cores and that of the transformer in accordance with this invention.

Before referring to the transformer of this invention, a widely used transformer utilizing an E and I type magnetic cores will be first described as one of the typical conventional miniature transformer. As is well known in the art said transformer is fabricated by the steps of laying up an E and an I type laminated cores one after the other to constitute a magnetic core, and providing a coil wound on the winding frame to said core. In said transformer a winding frame for winding said coil is an indispensable element and the use of which lowers the space factor of coil winding. Accordingly, when it is necessary to increase the winding volume of the coil, the core becomes necessarily large. This may be inconsistent with the recent tendency of miniaturization of various electronic machine parts. Furthermore, an inrease in the size of said core causes iron losses and the whole shape of the coil of the transformer utilizing an E and an I type cores becomes square thus making long the length of the core and causing greater copper losses thereby lowering the eificiency of the transformer compared with the round shape coil. Moreover, the disadvantages of the transformer utilizing an E and an I type cores reside not only in its square shape, but also in the electric characteristic because the gap at the contact of said E and I type cores increases the magnetic resistance thereby lowering the effective permeability of the magnetic cores.

In lieu of the above-mentioned transformer, such transformer as described in the United States patent specification (Patent No. 2,949,591) has been proposed. Said transformer is characterized by the cylindrical bobbin of insulating material on which a coil is Wound and the cylindrical sleeve is placed on said bobbin. Referring now to FIG. 1, thin magnetic material, such as a 45% or 78% nickel-iron alloy is cut to provide a core element 1 and two end flanges 2 and 3. A hollow 4 is provided coaxially to the central portion of said core element 1.

Ioreover, slits 5 and 6 are provided on said flanges 2 and 3 respectively to prevent eddy current. Thus, a bobbin is fabricated. After that, as shown in FIG. 2, a thin r layer of insulating compound 7 is applied to the rims of said core element 1 and the opposing inside of flanges 2 and 3. A coil 8 is wound on said thin layer of insulating compound 7 and lead wires 9 and ll of said coil 8 are respectively passed through said hollow 4 and taken out from said flanges 2 and 3. A cylindrical sleeve 12 shown in FIG. 3 is placed over the coil 8. Said sleeve 12 has a slit 13 along its longitudinal direction and the inner wall of said sleeve 12 is brought into contact with the outer rims 14 and 15 of said flanges 2 and 3 thereby fabricating a columnar transformer as shown in FIG. 4.

In manufacturing the above-mentioned columnar transformer, the following difficulties arise. First of all, a thin sheet of round rod shape magnetic material is cut as shown in FIG. 1 at the manufacturing process. This means that portions other than the bobbin are removed as unnecessary. It is therefore very wasteful. Furthermore, the shape of said bobbin is not suitable for the automatic cutting operation and mass production thus making it difficult to lower the price of the bobbin. In bringing the outer rims 14 and 15 of the flanges 2 and 3 of said bobbin into contact with the inner wall of said sleeve 12, the effective permeability is considerably lowered because of its thin flanges 2 and 3, large magnetic resistance and considerably great leakage flux. If the flanges 2 and 3 are made thick in order to eliminate the above disadvantages, the space factor for winding the coil is reduced.

There is another difliculty in fabricating said columnar transformer, viz., the production of the same standard of the sleeve 12 is somewhat difficult due to its cylindrical shape. Further, it is difficult to secure said sleeve 12 to the bobbin, thus the mass production of said sleeve is difficult.

Accordingly, the transformer in accordance with this invention is intended to eliminate the above mentioned various disadvantages of the conventional transformer. As shown in FIG. 5, circular flanges 21 and 22 are fabricated of any pipe-shaped magnetic materials of high magnetic permeability, such as permalloy or chromium-iron alloy by stamping or extending both ends of said magnetic materials.

Slits 23 and 2.4 for preventing eddy current are respectively providedto said flanges 21 and 22. Moreover, slit 26 is provided to the longitudinal direction of the cylinder 25, viz., between two end flanges 21 and 22 directly to said slits 23 and 24. FIG. 6 shows another embodiment of an inner core to be utilized in the transformer of this invention. Although said inner core 28 is substantially the same shape as that of the inner core 27 shown in FIG. 5, it is particularly designed for preventing eddy-current losses and a plurality of slits 29, 30, 31, 32 and 33 (though only four slits are shown in FIG. 6) are provided on said flanges 21 and 22 radially to the hollow 34. Reference is further made to FIG. '7 in which a still further embodiment of the inner core 37 to be utilized in the transformer of this invention is shown. More particularly, in lieu of the above-mentioned circular flanges 21 and 22, four .projecting fragments are provided to both ends of the cylinder 25 and said projecting fragments are bent perpendicular to the axial direction of said cylinder 25. Thus, flanges 35 and 36 are formed radially to the hollow 34. Furthermore, an inner core 38 shown in FIG. 8 shows a modification of the inner core 37 shown in FIG. 7 in which three projecting fragments are provided to both ends of the hollow cylinder 34 and said three projecting fragments being perpendicular to the axial direction of said hollow cylinder 34. An inner core 39 shown in FIG. 9 shows a still further embodiment of the inner core to be utilized in the transformer of this invention, wherein discoiclal flanges 41 and 42 are provided to both ends of the solid core element 40 of said inner core 39 fabricated of magnetic material of high resistivity, such as ferrite.

An outer core is formed as shown in FIG. 10 so that the inner walls of the outer core is brought into contact with the outer side of the flanges of each inner core, that is to say, perpendicular to the axial direction of the cylinder 25 shown in FIG. through FIG. 8 and the solid core element 40 shown in FIG. 9. More particularly, a box-like outer core 43 having one open face only on one side is fabricated of thin magnetic material of high magnetic permeability, such as permalloy or chromium-iron alloy by the stamping process. The dimension between the inner walls of the sides 45 and 4d or 47 and 48 of the outer core 43 is equal or somewhat small compared with the dimension between outer sides of the flanges of each inner core shown in the above FIGURES 5 through 9, thus making the magnetic resistance considerably small because the contact between the inner side wall of the outer core 43 and the outer side of the flanges of the inner core is sufficient. The state in which said outer .core 43 and each inner core shown in the FIGURES 5 through 9 are joined together is shown in FIG. 12. wherein the inner core is the same inner core 39 shown in FIG. 9. In this case, the magnetic path is formed in the direction in the order of solid core element 40 of the outer core 43, sides 4-5 and 46 of said outer core 43, a side 49 of said outer core 43, and the flange 41 of the inner core 39 or in the opposite direction of the above order. In this magnetic path, the portion in which eddy current frequently flows is the solid core element 40 of the inner core 39. Therefore, said solid core element 40 is expected to lower the effective permeability of the whole magnetic path because of its considerable inner volume.

However, the inner core 39 in accordance with this invention is fabricated of magnetic material of high resistivity in order to reduce eddy current losses. Moreover, as mentioned before, a space to be brought into contact by the side of the outer core and the flanges of the inner core utilized in the transformer of this invention is made as large as possible so that the magnetic resistance at the contact surface is small whereby the effective permeability of the core is considerably increased. Furthermore, as the contact surface is completely covered by the outer core, there is no leakage flux from the contact surface. Accordingly, the transformer of this invention is not under the influence of the magnetic flux from the outside.

The manufacturing process of the transformer of this invention will be illustrated on the basis of the magnetic path described above. Referring now to FIG. 11, an

insulating coating 49 is applied to the outer periphery of the cylinder 25 of the inner core 38 shown in FIG. 8 and each opposing face of the flanges 35 and 36. (It is to be understood that the insulating tape may be utilized instead .of said insulating coating 49 as desired). After that, as shown in FIG. 13 (the inner core shown in FIG. 13 is the same shown in FIG. 7), lead wires 51 through 55 .of said coil 50 are respectively connected to any lead terminals 57 through 62 provided on the terminal plate 56 fabricated .of insulating material, such as phenol resin. After connecting said lead wires to lead terminals, the coil 50 is fixedly secured to the curved portion 63 of the terminal plate 56 and at the same time the inner core 37 is fixedly secured within the outer .core as shown in FIG. 12. One embodiment of the external construction of the transformer of this invention manufactured above is shown in FIG. 14. As is clear from FIG. 14, the outer .core 43 serves also as a case and lead wires of the coil 50 are connected to lead terminals 57 through 62 provided on the terminal plate 56 so that said terminal may be directly mounted on the printed base plate and more- .over soldering is possible.

The result of the electric characteristic of the transformer of this invention fabricated as above is shown in the following by comparison with that of conventional transformer. The characteristic view shown in FIG. 15 shows the relation between the frequency and the insertion loss. More specifically, a curve of the solid line (a) in FIG. 15 is a characteristic view of the transformer of this invention and acurve of the dotted line (b) is that of the conventional transformer shown in FIG. 4. This figure clearlyshows that the transformer of this invention has a far bettercharacteristic in the low frequency region than the conventional transformer.

FIGS. 16 and 17 show the relation between the distortion factor and the frequency of the transformer utilizing an E and an I type cores, and the conventional transformer shown in FIG. 4 by measuring electric power as a parameter. While in these figures curves of dotted lines respectively show the relation between the distortion factor and the frequency of the conventional transformers, a curve of the solid line show that of the transformer of this invention. Thus, FIGURES l6 and 17 clearly show that the distortion factor in the low frequency region is considerably improved in accordance with the transformer of this invention. In other words, FIGURES l5, l6 and 17 show the improvement of the various characteristics in the low frequency region. Particularly, it must be pointed out that the improvement of the transmission characteristie in the low frequency region of the low frequency transformer of this invention contributes to the improvement of fidelity and output of the transformer. The improvement of these various characteristics is attributable to the improvement of the effective permeability due to the large contact surface between the outer core and the flanges of the inner core. The transformer of this invention has changed the idea of the conventional construction of the magnetic circuit of the low frequency transformer and has proved the improvement of the electric characteristic due to the revolutionary change of the construction of the above magnetic circuit.

FIG. 18 shows the difference between the shielding characteristic of the transformer of this invention and that of the conventional transformer utilizing an E and an I type cores. More particularly, a curve of the solid line shown in FIG. 18 shows the characteristic view of the transformer of this invention and a curve of the dotted line shows the characteristic view of the conventional transformer utilizing an E and an I type cores. As a measuring condition, an induced power in the uniform magnetic field of 1 oersted of 50 c./s. frequency is represented by lmW=OdB. The alphabetic letters in the characteristic view shown in FIG. 18 show the direction of the magnetic flux in the above two transformers. The maximum value of the shielding effect in the transformer is shown in the direction A-B which is under the maximum influence of the outside magnetic field. It is clear from FIG. 18 that the attenuation volume of the outside magnetic field in accordance with the transformer of this invention is 55dB and that of the conventional transformer is 48dB. It only proves that the shielding effect of this transformer is better than that of the conventional transformer by 7dB.

Although the relation between the shielding characteristic of the transformer shown in FIG. 4 (U.S. Patent No. 2,949,491) and that of the transformer in accordance with this invention is not shown, it is to be understood that the shielding effect of the transformer shown in FIG. 4 is inferior to that of the transformer of this invention because of its low effective permeability and the outside exposure of the contact surface of the bobbin and the sleeve.

From the foregoing it will be seen that the present invention provides a miniature transformer having little eddy-current losses, considerable effect permeability, improved transmission characteristic and good shielding effect by fixedly securing the inner core comprising a flange of relatively large contact area with the outer core and serving also as a winding frame to the box-like outer core of magnetic material, thus forming the magnetic path together with said outer core. Furthermore, as the thickness of said flanges may be considerably thin and the space factor of the coil is good, the transformer is miniaturized and the decrease of the iron-loss is realized. Moreover, the manufacturing of the inner and outer cores is easy because no such troublesome operation as cutting is required. Therefore, it is convenient for the automatic operation and mass production thus lowering the price,

While description and illustration of exemplarly embodiments of the present invention are made, it will become apparent that variations of the specific details of construction may be resorted to without departing from the true spirit and the scope of the invention as defined in the appended claims.

What is claimed is:

1. A miniature low frequency transformer comprising an inner cylindrical core fabricated of magnetic material, said cylindrical core having annular flanges which extend radially from each end of said cylinder, at least one winding with end leads, wound on said cylinder between said flanges, a terminal plate disposed in the vicinity of the cylinder provided with terminals for connecting each lead of said winding, and, a box-like outer core integrally fabricated of a single piece of solid thin sheet material having high magnetic permeability and having an open face on which said terminal plate is secured, said boxlike outer core having one selected pair of opposite sides of substantially the same inner dimension as the axial length of said cylindrical core, snugly fitting against the outer sides of said flanges, and, extending at least therebetween and being arranged so that the outer side of each flange and the inner surface of each opposite side are closely in contact with each other in order to form a magnetic path together with said inner core.

2. A miniature low frequency transformer as claimed in claim 1 wherein said inner core comprises a central hollow cylinder provided with an axial slit and flanges on both sides provided with at least one radial slit, and is integrally fabricated of a single piece of solid thin sheet material having high magnetic permeability.

3. A miniature low frequency transformer as claimed in claim ll wherein said inner core is solid, has circular flanges on both ends and is made of magnetic material of high resistivity.

4. A miniature low frequency transformer as claimed in claim 2, wherein each flange of said inner core comprises a plurality of radially projecting fragments that are bent perpendicularly to the axial direction of the cylinder.

References (Iited UNITED STATES PATENTS 2,775,742 12/1956 Bogue et a1. 33683 2,949,591 8/1960 Craige 336-178 X LEWIS H. MYERS, Primary Examiner. T. J. KOZMA, Assistant Examiner. 

1. A MINIATURE LOW FREQUENCY TRANSFORMER COMPRISING AN INNER CYLINDRICAL CORE FABRICATED OF MAGNETIC MATERIAL, SAID CYLINDRICAL CORE HAVING ANNULAR FLANGES WHICH EXTENDRADIALLY FROM EACH END OF SAID CYLINDER, AT LEAST ONE WINDING WITH END LEADS, WOUND ON SAID CYLINDER BETWEEN SAID FLANGES, A TERMINAL PLATE DISPOSED IN THE VICINITY OF THE CYLINDER PROVIDED WITH TERMINALS FOR CONNECTING EACH LEAD OF SAID WINDING, AND, A BOX-LIKE OUTER CORE INTEGRALLY FABRICATED OF A SINGLE PIECE OF SOLID THIN SHEET MATERIAL HAVING HIGH MAGNETIC PERMEABILITY AND HAVING AN OPEN FACE ON WHICH SAID TERMINAL PLATE IS SECURED, SAID BOXLIKE OUTER CORE HAVING ONE SELECTED PAIR OF OPPOSITE SIDES OF SUBSTANTIALLY THE SAME INNER DIMENSION AS THE AXIAL LENGTH OF SAID CYLINDRICAL CORE, SNUGLY FITTING AGAINST THE OUTER SIDES OF SAID FLANGES, AND EXTENDING AT LEAST THEREBETWEEN AND BEING ARRANGED SO THAT THE OUTER SIDE OF EACH FLANGE AND THE INNER SURFACE OF EACH OPPOSITE SIDE ARE CLOSELY IN CONTACT WITH EACH OTHER IN ORDER TO FORM A MAGNETIC PATH TOGETHER WITH SAID INNER CORE. 